Thermal expansion impulse actuator in plasma jet apparatus



Illll lllllllll i I I. HENINS ETAL Oct. 25, 1966 THERMAL EXPANSION IMPULSE ACTUATOR IN PLASMA JET APPARATUS Filed April 27, 1966 PLASMA JET APPARATUS wk m C DEY YPL m Hm 0 0 ws United States Patent 3,281,324 Patented Oct. 25, 1966 nice The invention described herein was made in the course of, or under, a contract with the US. Atomic Energy Commission.

The present invention relates to an electrically energied linear actuator capable of providing a precisely timed mechanical impulse.

Linear actuators capable of impulsively operating a gas valve find particular usefulness in gas plasma devices such as shown in Patent 2,961,559 issued to John Marshall on November 22, 1960.

The referenced patent shows an electromagnetic impulse type operator for a gas admittance valve. The impulse operator of the present invention is thermally energized and has the advantage of simplicity, cheapness and ruggedness over prior art valve actuators.

The actuator of this invention utilizes one or more elongated metal members having a positive temperature coefficient of expansion and through at least a part of which, a charged electrical capacitor is abruptly discharged. The I R heating occurs prior to any significant motion in the metal member so that the first effect after discharge of the capacitor is a compressive state in the metal member. The compressive state results in a shock initiated elongation wave in the metal member followed by rarification and a shrinking wave and a repetition of the cycle until the shock wave energy is dissipated. Only the original elongation wave and shrinking waves are used to ballistically operate the gas valve.

In practice, one end of the metal member or members, hereinafter called the driver member, is anchored in fixed spatial relationship with the valve to be operated. The lengthwise motion at the free end ballistically impels the valve to open condition. A restoring spring, or any other convenient biasing means is used to close the valve.

In order that the invention may be more fully understood, reference is made to the drawing in which is illustrated a lengthwise sectional view through a diameter of an impulse actuator made in accordance with the present invention.

A qualitative description of the behavior of the thermal eXpansion actuator of the present invention is as follows:

The rise in temperature of the driver element is essentially instantaneous and results in a momentary state of compression in the driver element. It the driver element is considered to have a length L at ambient temperature before the electrical discharge, immediately after the discharge it will contain potential energy tending to result in a new length equal to where AT is the temperature rise, and n is the thermal expansion coefiicient. The thermal expansion coefiicient of stainless steels containing about 79% nickel, 13% chromium, and 6% iron such as Inconel is about 1.5 X 10- Therefore, if an electrical discharge is chosen such as to give a 50 C. rise in temperature, a 50 cm. length of driver rod will exp-and finally by As stated above, the driver is not able to expand instantaneously and before expansion, contains a compressive force equal to 7.5 10 c 12 2 W X O 1500 kg. force/cm.

wherein the term 2x 10 is Youngs modulus.

A coaxial driver of two telescoped Inconel tubes, the outer of which has a /2" ID. and the inner of which has a I.D., and both having a 10 mil. thick wall, has a cross-sectional area of 0.18 cm The expanding force lengthwise in such a driver is 1500 x 0.18 :270 kilograms The driver rod will abruptly grow lengthwise a distance in excess of what the elongation would have been at the same final temperature if the heating had been slower by reason of inertial overshoot. The axial oscillation in length of the driver rod continues until damped out. In the application of this phenomena to ballistic opening of a gas valve only the first elongating excursion is used.

Referring to the drawing, a practical preferred embodiment is shown:

This impulse linear actuator comprises an outer tubular member 9 and an inner tubular member 11. A portion of the tubular members constitute the driver section and consists of coaxial conductors 13 and 15 which are electrically terminated at 17. The bridging conductor 17 is preferably a metal ring having good electrical contact with both tubular conductors. The tubular members, either one or both may extend beyond the driver section to the point of utilization of the mechanical impulse. In the embodiment shown, both tubular members extend to and are afiixed to gas valve base member 19. Gas valve base member 19 is slidably and hermetically supported in the associated utilization apparatus, which in this illustration is plasma jet apparatus.

The ends of the tubular members 9 and 11, opposite the utilization apparatus are firmly anchored in metallic terminal plates 21, 23. Plates 21, 23 serve the double functions of mechanical anchorage and electrical terminals. Pursuant to the function of electrical connection, plates 21 and 23 are insulated from each other by intervening electrical insulator 25. The two plates 21, 23 and the insulation plate 25 are aflixed to one another in any convenient manner such as by an adhesive bonding material. The plate and insulator assembly is fixedly supported relative to the utilization apparatus by bracket 27 and fixture 29. Fixture 29 is fixedly attached to the plasma jet apparatus housing 33 by any convenient attachment means such as the weld 31.

The valve mechanism comprises base member 19 and hollow poppet valve 35. Poppet valve 35 is provided with stem 3-7 which is slidably supported in valve base member 19. The free end of the valve stem is provided with compressed restoring spring 39 and keeper 41. The poppet valve normally rests in gas-tight relationship with base member 19. To facilitate a gas-tight relationship, a resilient sealing member such as O-ring 43 is affixed to one of the valve members and in the embodiment shown, the O-ring is aflixed to the poppet valve.

In operation, an electric charge is impressed across terminal plate members 21, 23, and transverses the inner and outer conductors 11 and 13 between the terminal plates and the shorting ring. The electric charge is almost instantaneously converted into heat energy, thereby generating an axial elongation shock wave in driver members 11 and 13. This elongation shock wave is coupled to the valve by extension portions 14, 16. The arrival of the shock wave blow at the valve base member 19 and poppet valve 35 results in both the base member and poppet valve being impelled in the direction of travel of the shock wave. The impulse is sufficient to cause the poppet valve to continue its motion after the motion of the valve base is terminated and reversed. Prior to activation of the valve, the interior of the hollow poppet valve head is provided with the desired gas through inner tubular conductor 11. Upon activation of the valve, the gas confined in the space provided in the poppet valve expands into the evacuated plasma jet apparatus.

In the embodiment shown, the tubular members in the driver portion are 6 in length. An electrical discharge from a 240 microfarad capacitor initially charged to 2.5 kilovolts is adequate to open the valve poppet at a velocity of about 10 meters per second with a total stroke of about 3 mm. which is limited by the return mechanism of the poppet. The desired stroke in any case is readily obtained by selecting a capacitor of suitable size charged to a selected potential such that the stored energy when discharged into the driver conductors is converted into the necessary number of calories of heat.

The drawing shows a preferred embodiment which has been used in practice, but it is apparent that many modifi cations are possible. For example, the driver conductor need not be a pair of coaxial tubes but could be a single tube or rod with one or more flexible electrical connections. The coupling mechanism between the driver and the utilization apparatus may have any convenient form. It is desired, therefore, that the invention be considered limited only by the appended claim interpreted in the light of the prior art.

What is claimed is:

A thermal expansion impulse actuator for actuating a gas valve in gaseous plasma jet apparatus with precision timing, comprising a driver member having a pair of coaxial metallic tubes, said metallic tubes having electrical terminals at one end and being electrically connected together at the other end, mechanical fixture means for fixedly and insulatingly supporting the terminal end of said tubes in a selected spatial distance from the plasma jet apparatus, said gas valve being a poppet type valve with a seat member hermetically and slidably supported on said plasma jet apparatus, and having a movable member having a hollow head and a stem, said seat member having an axial passage therethrough normal to the plane of the seat for slidably supporting the stem of the movable member, a rigid hollow mechanical means fixedly coupling at least one of the driver member coaxial tubes to the valve seat member, in register with he aforesaid axial passage, said valve stem slidably supported in said valve seat and spring means biasing said valve movable member in hermetically tight condition against said valve seat, gas supply means connected to the inner one of the coaxial metallic tubes to thereby fill the hollow head of said valve during quiescent intervals, whereby the sudden discharge of electrical energy into said electrical terminals results in opening said valve at a known time subsequent to the electrical discharge.

No references cited.

REUBEN EPSTEIN, Primary Examiner. 

